This invention is directed to an apparatus for providing a photographic stereogram. More particularly this invention is directed to a multi-objective lens camera for providing a plurality of photographic images which can be used to form a stereogram.
A photographic stereogram may be prepared by several methods: (1) a photograph taken with a normal camera having a single objective and moving it or the object to successive viewpoints; or (2) a photograph taken with a camera having a single objective and an optical stereo attachment which enables two photographs of an object to be taken simultaneously from two viewpoints; or (3) a photograph of an object with a camera having two objectives whose separation is equal to the normal sterescopic base of approximately 65 mm. A combination of any of the foregoing methods may also be used. Each of the photographs is photographically broken up into a series of narrow strips representing alternatively the picture of the left and right stereogram.
In each of the above methods the single or multiple camera objectives are directed to an aim point. The aim point is the point of convergence of the lenses in a multi-objective lens camera or the center of arc of a single lens camera rotating around the subject or the center of the subject rotating around during the camera exposure. The aim point is a vertical line within the image that will be at the rear surface of a superimposed lenticular screen when the finished picture is viewed. The aim point is therefore established and fixed before or when the photosensitive material is exposed. After exposure the aim point cannot be changed or adjusted.
A particular problem arises when the photography is of small objects at short range with a single objective lens. Movement of the camera to a second position usually requires a rotation in order that the object to be photographed may remain within the field of view. However, this rotation leads to undesirable distortions of the images. This parallax difference can be avoided if the optical axis of the objective lens remains always parallel to its original position and, of course, normal to the plane of the photosensitive material. The objective must be moved parallel to the photosensitive material without rotation of the optical axis and in such a direction as to reduce the length of the baseline between the positions of the lenses. A normal single objective camera, however, is of rigid construction and the objective cannot be moved.
Although the methods described for a single-lens camera are quite simple, nevertheless considerable time is required for accurate setting up of the apparatus; and in carrying out the steps in making two exposures. In addition, moving the object instead of the camera is impractical with remote objects, buildings and other motionless subjects or where the background is discontinuous and non-uniform.